Apparatuses and systems for density gauge calibration and reference emulation

ABSTRACT

Apparatuses and systems for emulating electrical characteristics of a material having a known dielectric response are disclosed for standardizing and calibrating of electromagnetic devices. The emulator apparatus can include an electrically non-conductive layer having a dielectric constant less than the material dielectric constant and an electrically conductive layer adjacent the non-conductive layer. Artificial dielectrics for emulating the dielectric response of a material are also disclosed including a substrate matrix having a dielectric constant less than the material dielectric constant and an additive combined with the substrate, the additive having a dielectric constant higher than the material dielectric constant.

RELATED APPLICATIONS

This application is related to U.S. Provisional Patent Application Ser.No. 60/663,420, filed Mar. 18, 2005; and is a continuation ofapplication Ser. No. 11/384,005 filed Mar. 17, 2006, now U.S. Pat. No.7,705,614 the disclosures of which are incorporated herein by referencein its entirety.

TECHNICAL FIELD

The presently disclosed subject matter relates to standardization andcalibration of electromagnetic devices. More particularly, the presentlydisclosed subject matter relates to apparatuses and systems foremulating electrical characteristics of a material having a knowndielectric constant.

BACKGROUND

Pavement materials, such as soil, sand, aggregate, asphalt, and cement,typically require quality control testing during the constructionprocess for physical attributes such as density, modulus, cementcontent, and moisture. The moisture and density relationship is animportant property that is monitored during road construction andrehabilitation. In order to provide durable roads, the soil base layerand all hot mixed asphalt layers above it are compacted to densityvalues that are specified in the engineering design. Destructive testsand nondestructive tests are used throughout the industry for qualitycontrol of these materials.

In laboratory tests, cylindrical samples are prepared, typically with agyratory compactor, and various material properties are studied todetermine the best mix design for a pavement. In field destructivetests, cylindrical samples are cored from test strips, newly constructedroads, or existing roads. The material properties of these samples arethen used to evaluate whether the test strip or the new pavement meetsthe design criteria and whether the existing road is in good operatingcondition or in need of repairs.

Currently, several methods are used for measuring the density ofcylindrical asphaltic samples including dimensional analysis, the waterdisplacement method, and the paraffin-coated or para-film-coveredmethod. In each case, the bulk density of a sample is derived by, as inthe definition, dividing the dry sample mass by the estimated samplevolume. All methods require a balance with a sensitivity of 0.1 gram tomeasure the mass of the sample.

In the dimensional analysis method, sample volume is determined fromradius and thickness (height) measurements of the sample. Here, manyreadings of radius and thickness of the sample are made either manuallyusing a vernier caliper or automatically using a laser system. Theaverage values of radius and thickness are then used to calculate thesample volume. Other methods use the Archimedes Principle related towater displacement for determining the sample volume. These methodsrequire a large container filled with clean water wherein the watertemperature is monitored and controlled at a specific temperature, e.g.at 25 degrees Celsius. The sample is kept immersed in water forapproximately 4 minutes during the test and the weight of the sample,while suspended in water, is recorded. In the “paraffin-coated” method,after determining the dry weight of the sample, a thin coating ofparaffin is applied to cover the entire surface area of the sample.Then, the sample is weighed again in air. Finally, the sample is weighedwhile immersed in water. More details can be found in standards ASTM D2726 for the water displacement method and ASTM D 1188 for theparaffin-coated method.

In the field, at present, the moisture content and density of materialsare typically determined using two non-destructive test methods. Onemethod uses radioactive materials or nuclear gauges and is commonlyknown as the “nuclear method”. The other method uses the electricalresponse of the material without radioactive materials, usingelectromagnetic devices, and is commonly known as a “non-nuclear” methodor the “electromagnetic method”.

Nuclear radiation gauges, such as those described in U.S. Pat. Nos.2,781,453 and 3,544,793 have been widely used for measuring the densityof soil and asphaltic materials and have been in use in the roadconstruction industry since the 1950's. Such gauges employ a nuclearradiation source, typically a mono-energetic source, which directs gammaradiation into the test material, and a radiation detector, typically aGeiger Mueller tube, located adjacent to the surface of the testmaterial for detecting radiation scattered back to the surface. Thegamma radiation interacts with matter in the test material, either bylosing energy and changing direction (Compton interactions) or byterminating (photoelectric interactions). Consequently, the gammaradiation detected by the radiation detector has a continuous energyspectrum. From this detector reading, the density of the material can bedetermined.

These gauges are designed to operate both in a “backscatter” mode and ina direct transmission mode. The radiation source is vertically moveablefrom a backscatter position where it resides within the gauge housing(e.g., the nuclear gauge rests on the surface of the pavement or soil)to a series of direct transmission positions where it is inserted intosmall holes or bores in the test material (e.g., the nuclear source isinserted beneath the soil surface, as in a borehole). The gammaradiation received by the radiation detector is related to the densityof the test medium by an expression of the following form:CR=Aexp(−BD)−Cwhere:

CR=count ratio (the accumulated photon count normalized to a referencestandard photon count for purposes of eliminating long term effects ofsource decay and electronic drift);

D=density of test specimen; and

A, B, and C are constants.

Nuclear gauges, however, require a high degree of training andradiological management for the operators of these gauges. Therefore,knowing of the desire to obtain accurate field measurement gaugeswithout the use of nuclear gauges, research began in the late 1980s intoelectromagnetic devices for measuring the density and moisture contentof road construction materials such as asphalt, soils and aggregates.These electromagnetic devices have different principles behind moistureand density measurements than their nuclear counterparts.

For moisture measurements in the field, the nuclear device methodincorporates neutron moderation, which results in a measurement of thenumber density of the Hydrogen atoms present in the material. Fornon-nuclear devices, the moisture measurement is based on the electronicdipole moment per unit volume of the material under test. Most asphalthas a permittivity of less than about 8 and is not terribly dispersivewith frequency. Typically, dry soil has an electrical permittivity ofabout 4, water about 80, and air about 1. In general, soil can havepermittivities that range from a dry value of about 4 to a saturatedvalue above 40. In soils, this parameter is frequency dependent. As thepercent water increases in sand, soil, aggregate, etc., the dielectricconstant increases as well. Therefore, the moisture content can beeasily found by measuring the electrical properties of the material. Amuch more complicated process is required for simultaneous measurementof moisture and density values.

For density measurements in the field, the nuclear device method usesgamma ray scattering properties of the materials. At energies below 1MeV, the amount of scattering in a material is directly proportional tothe number density of electrons. Since the number density of electronsis related to the material density, by measuring the scattering, thematerial density is found. The electromagnetic device method usespermittivity changes resulting from the decrease in the air void contentof an asphalt mix as it is compacted. Therefore, asphalt density can beestimated by measuring the permittivity of the mix.

Asphalt is a heterogeneous mixture of aggregate, binder, and air. Soilis much more complex and is a mixture of aggregate minerals, air, andwater. Air has a dielectric constant ∈_(r) of 1.0, whereas dry aggregateand binder dielectric constant ∈_(r) is about 4.0. Water has adielectric constant ∈_(r) of near 80 depending on the temperature andpurity of the water. The dielectric constant or permittivity isrepresented by a complex number where the real part represents theenergy stored and the imaginary part represents the energy loss in thematerial. For asphalt, as compaction increases and the densityincreases, the air voids decrease and the dielectric constant increases.As such, asphalt is mostly moisture free and usually has a simplefrequency response. For soil, increasing compaction efforts alsoincreases the dielectric constant. However, soil is a complexheterogeneous mixture of air, water, and solid minerals that has a verycomplex frequency response that complicates the response. As a result,for soil, measurements of the real and imaginary parts of thepermittivity are required to separate the moisture from the densityeffects. Hence, the frequency response of these materials is also ofmajor interest.

For a given soil, the maximum compaction is achieved at specificmoisture content. In the laboratory, the density-moisture contentrelationship for a soil is determined using the industry standard“Modified Proctor Method”, otherwise known as ASTM D 1557 or the“Standard Proctor Method” known as ASTM 698.

For asphalt, in the laboratory there are three methods ofdesigning/analyzing asphalt mixes: (1) The Marshall method; (2) theHveem method; and (3) the Superpave method. All three methods producecylindrical asphalt cores for analysis. One of the most importantfactors is the material density, which is a primary property in theselection of the best mix design. The material density of cylindricalasphalt specimens is determined using dimensional analysis (mass overvolume) or variations of water displacement methods as specified in ASTMstandards D 1188 and D 2726.

A particular asphalt mix will contain unique aggregate types, textures,binder, and also contain air voids. For instance, the aggregate may beone of limestone or granite, and have proportions of size and texturefrom passing the 200 sieve to 25 mm. As a result, the base dielectricconstant of a high air void mix may be 4 for one mix and 7 for another.Furthermore, the dielectric constant will only change a small percent asthe air void content is decreased by compaction. For example, low tohigh density may range from 4.0 to 4.7 in the real part of thepermittivity.

FIG. 1 illustrates different mixing series and how they encompassdifferent “base” dielectric constants for each mix. In FIG. 1, each linerepresents the entire dielectric range from low to high density of thatspecies or mix. Furthermore, although there are different intercepts foreach mix, the slopes are not much different. The mixes shown in FIG. 1include both granite and limestone aggregates.

As discussed above, the industry has recently become interested inelectromagnetic devices for quality testing of pavement materials.Examples of such electromagnetic devices include Model M2701Bmanufactured by Troxler Electronic Laboratories, Inc., the assignee ofthe present subject matter, and Model PQI 301 manufactured by TransTechSystems, Inc. Both of these gauges use a single frequency (continuous)source which can be modulated, wherein the M2701B operates at about 50MHz and the PQI 301 operates at a much lower range frequency. Thesedevices are planar in that they are placed on top of the surface to bemeasured and fringe a field of energy into the material of interest.Typically, a high frequency electrical signal is passed through thecapacitive-sensor placed on the testing material. The signalcharacteristics measured by electrical signal detection circuitry arethen compared with those obtained by placing the sensor on knownmaterials. A correlation to the material density is then used toestimate the density.

Other electromagnetic devices include the TDR as sold by Durham GeoSlope Indicator; ground penetrating radar or GPR; resistive devices suchas that marketed by Humbolt and described in U.S. Patent ApplicationPublication No. 2004/0095154; swept or stepped frequency devices such asthat manufactured by Greer and described in U.S. Pat. No. 6,388,453; andmicrowave systems including systems described in U.S. Pat. Nos.6,316,946 and 5,952,561 and U.S. Patent Application Publication No.2005/0150278. Electromagnetic devices that operate in the “backscatter”as well as “transmission” mode are also envisioned with bandwidths ofseveral GHz, such as the device described in U.S. Patent ApplicationPublication No. 2005/0150278.

Moisture sensors can be stand-alone versions as well as dualdensity/moisture probes. Two examples of the stand-alone moisture probesare capacitance monitors for soil moisture as described in U.S. Pat.Nos. 5,260,666 and 4,929,885; each of which is assigned to the assigneeof the present subject matter, Troxler Electronic Laboratories, Inc.Another class of electromagnetic moisture probes is manufactured byHydronix.

Because of variations in manufacturing tolerances, sensing probes of thesame design will not necessarily sense exactly the same values.Consequently, each sensing probe must be individually calibrated at themanufacturing factory and as a practical matter the probe should beperiodically checked (or recalibrated) to assure that the calibrationhas been maintained.

For nuclear gauges, calibration is typically conducted using three largeand heavy blocks of material of different densities. Typically, theseblocks are aluminum (160 lbs/ft³ or PCF), magnesium (110 lbs/ft³), and amix of aluminum and magnesium (135 lbs/ft³). Other prior art in nuclearcalibration devices include shielded capacitance standards asmanufactured by Troxler Electronic Laboratories, Inc. and described inU.S. Pat. No. 4,924,173.

Electromagnetic gauges are typically factory calibrated using threelarge slabs or calibration standards (e.g., of a size 2 foot by 1 footby 6 inches thick) of varying dielectric constants. Three reference datapoints are obtained and a least squares fit is applied to the datapoints for the straight-line equation. It is noted, for example, thatthe three calibration standards typically span the entire dielectricrange shown in FIG. 1. In other words, an offset is usually necessary,but the slopes are going to be close to the expected field value.

Since the electromagnetic density gauges as known in the art are alsooperated on hot materials in the field, it is possible for theelectrical properties of the sensor to change with use and time. Also,any changes in the components in the electrical circuitry of the gaugecan lead to drifts in the detected electrical signals. Although thegauges have been designed to minimize these problems, the net effect canbe significant to the user. As such, the electromagnetic gauges shouldperiodically be recalibrated in the laboratory.

Electromagnetic gauges are typically recalibrated in the laboratoryusing bulk homogeneous materials of known electrical properties such asplastic, NYLON, PVC, PLEXIGLAS, and glass, to name a few. Thesematerials are typically in the form of slabs with dimensions 12 inchesby 12 inches by 6 inches wherein the weight of the standard can approach130 pounds or more. Standards can also be calibrated using cylindricalspecimens, much like the cores drilled in the field or made in the lab.In any case, the gauge is placed on each material and the signalcharacteristics are recorded. Using a mathematical model that relatesthe signal characteristics to the assigned density value, thecalibration coefficients are then determined. The systematic errorsdetermined can be corrected in the laboratory using the calibrationstandards. The measurements taken on the standards will show the changesand if the changes are small enough, adjustment to the calibrationcoefficients can be made. Hence, confirmation readings obtained on thestandards will indicate if recalibration or a simple offset will benecessary. It is additionally known that many regulatory agencies nowrequire that electromagnetic gauges have a reference standard forobtainment of these confirmation readings.

The response of electromagnetic gauges is related to the electricalproperties of the material being tested. Therefore, calibration of thedevices must typically be performed in the field at regular periodicintervals for determining the density and moisture content of materials.This calibration is typically correlated to known standards. Forexample, with density gauges, FIGS. 2A and 2B show the comparison ofgauge readings of factory-calibrated gauges to true density values forvarious asphalt mixes (FIG. 2A relates to limestone mixes and FIG. 2Brelates to granite mixes). Conversion of the direct reading to theabsolute density reading can be performed using cores extracted from thepavement or nondestructively by comparing and correcting using a nuclearmethod.

For instance, the calibration equation for the M2701B device can beselected for different mix types as found empirically in the field. Forexample, the operator can do simple offsets or a full-blownslope-intercept calibration to arrive at the calibration equation. Thisis sometimes achieved using a “test” strip wherein cores are removedfrom the test strip with different compaction efforts. Other times, agood compaction effort is made and a core is removed and gauge read. Thegauge is then offset with one core. Here, for example, the operatorwould obtain a reading using the M2701B device, remove a core sample,and test it for density properties in the laboratory. Another well-knownmethod is to obtain simultaneous readings using both a nuclear gauge andthe electromagnetic device. The nuclear results are used to obtain thecalibration in the electromagnetic device. The calibration in the gaugefor a simple mix is therefore a simple “y=mx+b” equation or even a“y=a+b*exp(−c*x)” relationship as is currently being explored. A singlecore or an average of multiple cores can be used for a simple offset. Ifa good spread of densities is obtainable, then both slope and interceptcan be calculated using standard methods.

It is known that electromagnetic devices must also be referenced(calibration confirmed) in the field preferably daily to account for anydaily variances encountered. In order to provide this capability in thefield, for example, the Model M2701B comes with a “portable”standardization block as shown with reference to FIGS. 3 and 4. As shownin FIG. 3, this standard block S is typically made out three (3) slabsof glass G, each typically having dimensions of 6 inches wide by 6inches long by 0.5 inches thick, wherein the slabs of glass G are gluedtogether. Typically, a thin layer of FR4 glass epoxy laminate L isoverlaid on top of the glass slabs to provide protection to the glass.The standard block S is typically installed with top and bottom layersof foam F in a carrying case C for the gauge device D (see FIG. 4showing laminate L overlaid on standard block S).

There are several limitations of this prior art standardization block Sincluding: (1) fragility—because of the nature of glass it is possibleto damage the block during transport of the gauge, thus leading toerroneous readings; (2) manufacturability—several steps that involvegluing using extremely hot glue are required including one operationgluing the standard to shock absorbing thick foam material, anotheroperation gluing foam to the bottom of the case, and another operationgluing a thin FR4 sheet on the top surface of the glass; (3) cost—thetype of special glass used for the standard is expensive; (4) weight—theglass-stack standard alone is about 5 lbs.; (5) size—the standard isonly slightly bigger than the gauge sensor head; (6) volume—the glassand foam occupy a large space in the case; (7) stability—due to theweight and cumbersome size of the standard, the glue can loosen overtime thereby providing erroneous readings; and (8) accuracy—due to thefinite thickness of glass (1.5 inches), the gauge reading shows a smalldependence on the type material on which the standard is placed.

Thus, there remains a long-felt need for apparatuses and systems ofdensity gauge emulation for the standardization of electromagneticgauges in the field using easy to manufacture, low cost, durablematerials with improved stability during transportation.

SUMMARY

The apparatuses and systems of the present subject matter relate tocalibrating and confirming the calibration and operation of non-nuclearmoisture-density quality control equipment, such as electromagneticdevices. The apparatuses can include a surface for supporting the gauge,and a material composite for simulating the dielectric properties of aconstruction material. The composite can consist of a matrix ofconducting and non-conducting material sometimes referred to as anartificial dielectric. It is envisioned that surface gauges, as well assurface probing instruments, can be calibrated, re-calibrated orconfirmed for operational standards.

Disadvantages of prior art calibration block systems include weight,bulkiness, and limited range of permittivity. With the apparatuses andsystems of the present subject matter, lightweight, economical standardsare available of considerable smaller volume. The emulator apparatusesand systems of the present subject matter have the ability toartificially decrease the size of typical reference standards, andartificially increase the effective dielectric constant of standards byadding materials near the sensor and embedded in the dielectricmaterial. Positive attributes of the apparatus of the present subjectmatter include: (1) the ability to be used with devices that sit on thesurface or just above the surface of the material being measured; (2)lightweight and field portable; (3) can easily be integrated into acarrying case for the gauge it is used with; (4) can exhibit a frequencyresponse tailored to a response of a heterogeneous material like soilwith particular dispersive properties; and (5) can be used with devicesthat are inserted into the soil or other material being tested.

It is envisioned that apparatuses and systems of the present subjectmatter can be used for the calibration of low frequency instruments,including static or quasi-static instruments, as well as high frequencyinstruments (into the microwave region). Due to the complexity of thefrequency response of heterogeneous mixes of materials like soil andwater, a wide band response measuring both the real and imaginary partsof the permittivity is sometimes necessary. This wideband response makesit possible to obtain multiple parameters such as density and moisturein soil.

In one embodiment of the present subject matter, an emulator apparatusfor emulating electrical characteristics of a material having a knowndielectric constant is provided. The emulator apparatus can comprise anelectrically non-conductive layer having a dielectric constant less thanthe material dielectric constant and an electrically conductive layeradjacent the non-conductive layer.

In another embodiment of the present subject matter, a combinationcarrying case and emulator apparatus is disclosed. The combination cancomprise a housing adapted for containing a dielectric sensitive probewherein the housing has a base and a closeable cover. The combinationcan further comprise an emulator apparatus disposed within the housingfor emulating electrical characteristics of a material having a knowndielectric constant, wherein the emulator apparatus can include anelectrically non-conductive layer having a dielectric constant less thanthe control material dielectric constant and an electrically conductivelayer adjacent the non-conductive layer.

In yet another embodiment of the present subject matter, a system forcalibration of a dielectric sensitive probe to account for changes ingauge geometry and other factors affecting gauge calibration accuracy isdescribed. The system can comprise a plurality of emulator apparatusesfor emulating electrical characteristics of a plurality of materialshaving different known dielectric constants. Each of the plurality ofemulator apparatuses can comprise an electrically non-conductive layerhaving a dielectric constant less than the associated one materialdielectric constant and an electrically conductive layer adjacent thenon-conductive layer.

In a further embodiment of the present subject matter, an artificialdielectric for emulating the dielectric constant of a material isprovided. The artificial dielectric can comprise a substrate matrixhaving a dielectric constant less than the material dielectric constantand an additive combined with the substrate, the additive having adielectric constant higher than the material dielectric constant.

In a still further embodiment of the present subject matter, anartificial dielectric for emulating the frequency dependence of amaterial having a known dielectric constant is described. The artificialdielectric can comprise a liquid mixture comprising at least one partliquid having a dielectric constant less than the material dielectricconstant and at least one part liquid having a dielectric constanthigher than the material dielectric constant.

In another embodiment of the present subject matter, an adjustableemulator apparatus for emulating electrical characteristics of amaterial is provided. The emulator apparatus can comprise anelectrically non-conductive layer having a dielectric constant and anadjustable electrically conductive layer adjacent the non-conductivelayer and defining an air gap there between. The conductive layer isadjustable toward the non-conductive layer to increase the measureddielectric constant and is adjustable away from the non-conductive layerto decrease the measured dielectric constant.

In yet another embodiment of the present subject matter, an emulatorapparatus for emulating electrical characteristics of a material havinga known dielectric constant is provided. The emulator apparatus cancomprise a first electrically non-conductive layer having a dielectricconstant approximately equal to the material dielectric constant and atleast one second electrically non-conductive layer having a dielectricconstant greater than or equal to 1.0, the at least one secondnon-conductive layer adjacent the first non-conductive layer.

In a further embodiment of the present subject matter, a combinationcarrying case and emulator apparatus is described. The combination cancomprise a housing adapted for containing a dielectric sensitive probewherein the housing has a base and a cover. The combination can furthercomprise an emulator apparatus disposed within the housing for emulatingelectrical characteristics of a material having a known dielectricconstant, wherein the emulator apparatus can comprise a firstelectrically non-conductive layer having a dielectric constantapproximately equal to the material dielectric constant and at least onesecond electrically non-conductive layer having a dielectric constantgreater than or equal to 1.0, the at least one second non-conductivelayer adjacent the first non-conductive layer.

Therefore, it is an object of the present subject matter to provideapparatuses and systems for emulating electrical characteristics of amaterial having a known dielectric constant for the standardization andcalibration of electromagnetic gauges.

Several objects of the presently disclosed subject matter having beenstated hereinabove, and which are addressed in whole or in part by thepresently disclosed subject matter, other objects will become evident asthe description proceeds when taken in connection with the accompanyingdrawings as best described hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating true density in relation to permittivityfor different mixing series of aggregates such as those measured bygauges used in conjunction with the reference emulator of the presentsubject matter;

FIGS. 2A and 2B illustrate a comparison of gauge readings offactory-calibrated gauges to true density values for various asphaltmixes such as those measured by gauges used in conjunction with thereference emulator of the present subject matter;

FIG. 3 is a side profile view illustrating a prior art standardizationblock;

FIG. 4 is a photograph illustrating a prior art standardization blockinstalled in a carrying case of an electromagnetic gauge;

FIGS. 5A-5D are perspective views of prior art artificial dielectricstructures (Collin);

FIGS. 6A-6B are schematic and electrical diagrams of a capacitive devicemeasuring a medium with and without a conductor, respectively, in thefield proximity;

FIG. 7 is a graph illustrating dielectric constant ∈ in relation tofrequency (MHz) for different types of soils such as those measured bygauges used in conjunction with the reference emulator of the presentsubject matter (Arulanandan);

FIG. 8 is a cross-sectional view of a reference emulator in accordancewith an embodiment of the present subject matter;

FIG. 9 is a top view of a reference emulator in accordance with anembodiment of the present subject matter;

FIG. 10 is a photograph illustrating a reference emulator installed in acarrying case of an electromagnetic gauge in accordance with anembodiment of the present subject matter;

FIGS. 11A-11C are top plan and cross-sectional views of a referenceemulator calibrator consisting of reference emulators of varyingmaterials with the same thickness in accordance with an embodiment ofthe present subject matter;

FIG. 12 is a cross-sectional view of a reference emulator calibratorconsisting of reference emulators of varying thickness of the samematerial in accordance with an embodiment of the present subject matter;

FIG. 13 is a cross-sectional view of a reference emulator calibratorconsisting of hinged non-conductive plates in accordance with anembodiment of the present subject matter;

FIG. 14 is a side profile view of a reference emulator comprising amechanically adjustable conducting plate in accordance with anembodiment of the present subject matter; and

FIG. 15 is a perspective view of a plurality of artificial dielectricspecimens for calibration of electromagnetic gauges in accordance withan embodiment of the present subject matter.

DETAILED DESCRIPTION Background of Artificial Dielectrics

Artificial dielectrics are basically large-scale models of a dipolarmolecule, constructed by arranging conductors in a 3-D pattern. Alightweight binder of filler material such as polystyrene supports theconductors. The result is a manmade material that simulates an ordinarydielectric material with a dipole moment. The combined effect of all theindividual conductors of the lattice is to produce a net dipolepolarization P per unit volume. Artificial dielectrics are discussedextensively in the art, such as by W. E. Kock in “Metallic Delay Lines,”Bell System Technical Journal, vol. 27, pp. 58-82 (1948) and by RobertE. Collin in “Field Theory of Guided Waves,” Second Edition, IEEE Press(1991).

As shown in FIG. 5 (Collin), there are many shapes of conductors thatone can use for artificial dielectrics, such as disks, needles, spheres,cylinders, etc. incorporated into a matrix. FIG. 5A illustrates athree-dimensional sphere medium; FIG. 5B illustrates a three-dimensionaldisk medium; FIG. 5C illustrates a three-dimensional strip medium; andFIG. 5D illustrates a three-dimensional rod medium. While FIGS. 5A-5Dare shown as three-dimensional systems, it is understood that they couldbe configured as two-dimensional systems.

In the case of metal strips loaded periodically in a substrate (such asin FIG. 5C), the dielectric constant is anisotropic since theorientation of the electric field vector E can result in capacitiveloading if perpendicular to the faces of the strips, or inductiveloading if the fields are parallel to the faces. For the perpendicularcase, the dielectric constant is increased resulting in what is alsoknown as phase delay media. For the case where the strips behaveinductively, (electric fields parallel to the faces), the magneticmoment leads to a reduction in the permeability. This is sometimesreferred to as a phase-advance dielectric.

For electromagnetic devices such as the TROXLER M2701B (operated in VHFrange) or TRANSTECH PQI 301 (operated in low frequency range), anartificial dielectric such as in FIG. 5C can be made simpler by joiningthe metal strips together in a sheet or plate. Alternatively, separatemetal strips can be mounted with a board or other substrate on thebottom. While electromagnetic devices such as the M2701B or PQI 301 canbe based on different operating principles (the M2701B measures couplingfrom one strip to another while the PQI 301 measures the capacitance),they each can be calibrated or referenced with these types of plates.

FIGS. 6A and 6B show general diagrams of a capacitive device like thePQI 301 measuring a medium with and without a conductor in the fieldproximity. FIG. 6A depicts a sensor on infinite medium ∈_(r) betweennodes 1 and 2 with no conductor and where C₁₂ is the externalcapacitance known as the mutual partial capacitance. This is the resultof the sensor field energy fringing into the asphalt or soil. C₁₀ andC₂₀ are parasitic capacitances that should be minimized for a goodsensor design. C₁₀ is the capacitance to ground of one conductor, whileC₂₀ is the capacitance to ground of another conductor. The signal groundG, represented by the node 0, could be a system ground, or isolatedusing electronic techniques, or it may act as a shield. C₁₂ representsthe field energy of the desired measurement. Shields are sometimesincorporated so that changes in the dielectric constant ∈ external tothe sensor result in measurements of C₁₂ as opposed to changes in C₁₀ orC₂₀.

FIG. 6B depicts a floating conductor brought into proximity of twoconductors, such as ground G (node 0) and plate P (node 3). In FIG. 6B,the conducting plate P is added at the bottom and the calibration deviceis bounded by conductor nodes 1 and 2 and conducting plate P (node 3).The network model shown in FIG. 6B results in C₁₂ being in parallel withthe series capacitance C₁₃ and C₂₃. Hence, the coupling increases as theeffective stored energy in the dielectric medium increases as modeled.In FIG. 6B, the effective capacitance is:C _(eff) =C ₁₂+(C ₁₃ *C ₂₃)/(C ₁₃ +C ₂₃)

C_(eff) is generally greater than C₁₂ and therefore the effectivecapacitance and thus dielectric constant has increased. As such, ifinsulated from ground in this manner, the additional conductor acts toincrease the measured capacitance coupling between nodes 1 and 2. It isnoted that the permittivity of the medium does not change, it isartificially increased by the proximity of the conducting plate P.C_(eff) is a function of ∈_(r) and t where ∈_(r) and t are bounded bynodes 3 and nodes 1 and 2.

In addition to the creation of an artificial dielectric by a sheet or aplate, another important method to obtain synthetic dielectrics isthrough the use of mixtures. One example would be to load a stycastepoxy with a high dielectric powder such as BaTi or TiO2. Manufacturerssuch as Cuming Corporation and Master Bond supply artificial dielectricsand ceramic filled epoxies such as these. Other companies sell atwo-part epoxy loaded with a dielectric powder. These epoxies can beused to manufacture cylindrical standards to synthesize asphalt corestaken from the road or made in a gyratory compactor.

Liquids can also be used to model natural heterogeneous dielectricmaterials such as the soil profiles shown in FIG. 7 (Arulanandan).Soil/water mixtures have a complex frequency response that depends onthe relative cohesiveness of the soil type and FIG. 7 illustratesmeasurements of the permittivity of different types of soils (e.g.,cohesive soils such as clay mineral and non-cohesive soils such assand). Soil can be modeled using an emulsion of water and oil. Manyother types of mixtures such as gelatin, alcohol, etc. are alsoenvisioned. Through mixture theory, these artificial materials will haveadjustable dielectric properties for the real and complex parts ofpermittivity, including the frequency dependent parameter referred to asdispersion. For radiating devices, it is sometimes desirable to scalethe model. For example, an antenna of higher frequency can mimic thelower frequency device if the proper scaling of the materials anddimensions surrounding the antenna is adapted. In practice, one mayplace a calibration probe into an analyzer (for solid/asphalt density ormoisture), and insert the antenna into a small calibration tank.Impedance is obtained in this tank at a higher frequency, and then amapping to the lower frequency device is performed. The tank in thiscase may also be surrounded with an absorbing material to simulate aninfinite medium or half-space.

One of the many mixing formulas that has been successful in the art isby Briggeman as reported in “Dielectric Behavior of HeterogeneousSystems”, Chapter 3, Progress in Dielectrics, Vol. 7 (1967). For oil inwater emulsions at frequencies less than about 3 GHz, it has been shownthat 3 parameters ∈, σ, and F are used in the equations and representthe low frequency permittivity, conductance and frequency dependence,respectively. The conductivity of the solution is adjusted by changingthe concentration of an electrolyte, such as sodium chloride. Mineraloil and water along with an emulsifier are used to adjust the dielectricconstant. Briggeman's mixing formulas also have been shown to apply tothe complex relative permittivity wherebyξ_(r)=ξ_(r) ′+jξ _(r)″≡∈_(r) −jσ/ω∈ _(o)where sigma is the conductance, omega is the frequency in radians persecond, and ∈_(o) is the permittivity of air. Briggeman's formula forlossy dielectrics becomes(ξ_(r)−ξ_(r1))³/(ξ_(r2)−ξ_(r1))=(1−Φ)³*ξ_(r)/ξ_(r2)where ξ_(r1) and ξ_(r2) represent the disperse particle phase and thematrix phase, respectively, and Φ is the volume fraction of the dispersephase. By solving this equation for specific dielectric constants andconductance, soils such as clay can be synthesized including thefrequency response. With proper mixing and materials, calibrationstandards for soils can be synthesized.

Emulator Apparatus

In accordance with the present subject matter, an emulator apparatus isenvisioned for providing a low-cost, lightweight, easily adaptablesubstitute for standardization blocks used in the prior art (see FIGS. 3and 4). It has been observed that when an electromagnetic gauge isplaced on a non-conducting material of dielectric constant ∈ in the formof a slab with thickness t, the signal amplitude detected by the gaugeis larger when the bottom surface of the material is covered with aconducting material. Thus, by selecting ∈ and t, this composite slab canbe used to emulate the dielectric property of material of much higherdielectric constant than the sum of the parts. This includes materialsthat can be used for gauge standardization (calibration confirmation) aswell as calibration or recalibration of the gauge (in the field orotherwise).

With reference to FIG. 8, a reference emulator, generally designated100, is shown in accordance with one embodiment of the present subjectmatter. Emulator 100 is capable of emulating the electricalcharacteristics of a material having a known dielectric constant andtypically comprises an electrically non-conductive layer (dielectric)102 having a dielectric constant less than the known material dielectricconstant and an electrically conductive layer 104 adjacentnon-conductive layer 102. Electrically non-conductive layer 102 can be aplate constructed of any non-conductive material, such as, for example,fiberglass, plastics, ceramics, polymers, glass, and composites thereof.Electrically conductive layer 104 can also be a plate constructed of anyconductive material, such as, for example, aluminum, copper, nickel,tin, silver, and steel. Non-conductive layer 102 and conductive layer104 can be joined together by any method of joining two substrates, suchas, for example, gluing. Furthermore, a thin, absorbent lossy layer 106can be optionally positioned between non-conductive layer 102 andconductive layer 104. Lossy layer 106 can operate to reduce effects ofair gaps, etc. sometimes experienced once non-conductive layer 102 andconductive layer 104 are joined together.

Referring further to emulator 100 illustrated in FIG. 8, several exampleemulator embodiments were designed using varying materials andthicknesses of non-conductive layer 102 and conductive layer 104 asfollows.

In a first example, a Model M2701B gauge manufactured by TroxlerElectronic Laboratories, Inc. was used to assign densities to four (4)emulators made with PVC as dielectric non-conductive layer 102 (varyingin thickness) and a sheet of 0.025 inch thick aluminum as conductivelayer 104. As shown in the table below, the measured densities atdifferent thicknesses of non-conductive layer 102 covers the entireoperational density range of the gauge.

Thickness of the Emulated Emulator dielectric material in Density No.non-conductive layer (inch) (lbs/ft³) 1 1.000 109.2 2 0.750 117.8 30.500 139.0 4 0.375 161.1

In a second example, a Model M2701B gauge manufactured by TroxlerElectronic Laboratories, Inc. was used to assign densities to two (2)emulators made with 0.75 inch thick DELRIN or FR4 as dielectricnon-conductive layer 102 (i.e., same thickness but different material)and a sheet of 0.025 inch thick aluminum as conductive layer 104. Themeasured densities were as follows.

Dielectric Emulated Density material (lbs/ft³) DELRIN 126.0 FR4 142.0

In a third example, a Model M2701B gauge manufactured by TroxlerElectronic Laboratories, Inc. was used to assign a density to anemulator comprising a one-side copper cladded 8 inch×8 inch×0.75 inchFR4 slab. In this embodiment, the FR4 material worked as dielectricnon-conductive layer 102 and the very thin copper plating worked asconductive layer 104. The measured density for this composite was 150lbs/ft³.

While FIG. 8 illustrates non-conductive layer 102 and adjacentconductive layer 104 in a composite plate configuration to form emulator100, it is also envisioned that the reference emulator of the presentsubject matter could be of a cylindrical configuration as shown in FIG.9. In FIG. 9, emulator 120 is also capable of emulating the electricalcharacteristics of a material having a known dielectric constant and cancomprise an electrically non-conductive layer 122 having a dielectricconstant less than the known material dielectric constant andelectrically conductive layers 124A, 124B adjacent non-conductive layer122. In this embodiment, conductive layers 124A, 124B consist of anouter shell (124A) and a center radius (124B) and surroundnon-conductive layer 122. It is understood that a plate on the bottom(not shown) could also be a conductor, and the shown metallic sections124A, 124B could be insulators as well. For example, center radius 124Bcould be a dielectric material and outer shell 124A could be aconductor. Alternatively, outer shell 124A and center radius 124B couldbe of a higher dielectric constant than middle layer 122, thus forming amatrix.

Referring to FIG. 10, it is contemplated that an emulator of the presentsubject matter, such as emulator 100 shown in FIG. 8, can be combinedwith a carrying case C (such as shown in FIG. 4) that is used to house adielectric sensitive probe, such as electromagnetic device D. Thecarrying case can comprise a base B and a closeable cover CC and can beconstructed of any material as known in the art, such as metal ormoldable plastic. Foam material F can further be included in thecombination in order to provide protection to device D. This combinationwould allow the improved reference emulator to be carried into the fieldwith the electromagnetic device for field referencing without thenecessary weight and bulkiness seen in existing referencestandard/carrying case combinations.

As discussed above, the emulator apparatus of the present subject matterhas many advantages over the prior art. Since the thickness necessary issmaller than for bulk materials, the reference plate area can beincreased without substantially increasing the weight of the entireunit. For example, for standardization (calibration confirmation) of anelectromagnetic gauge, an 8″ by 8″ reference slab (instead of the 6″ by6″ slab of the prior art design) can be used without a substantialincrease in weight. This ability to increase the reference plate areaminimizes errors from spatial variability of the signal characteristicsof the gauge, a disadvantage found in using existing reference standards(the conductive layer also eliminates the influence of the bottom earthlayer on the measurement). Other advantages include: lower cost formaterials due to the wide range of commercially available polymermaterials that are suitable for the purpose of reference emulation inaccordance with the present subject matter; less fragile than currentreference standard designs (which typically are made of glass); and easein manufacturing due to less components needing to be assembled than incurrent designs.

It is envisioned that the emulator apparatus of the present subjectmatter can be used with varying types of electromagnetic devices. Forexample, some devices use a radial or coaxial configuration with adielectric layer sandwiched between radii r₁ and r₂. As the dielectricthickness reduces, the effective dielectric constant will increase.Other instruments utilize resistive techniques. Still other methods,such as the time domain reflectometry (TDR) method, are based on wavepropagation velocity and signal attenuation. In the TDR method, a wavepropagates along a transmission line. The higher the dielectricconstant, the slower the wave and the longer it takes for the signal toreturn. By knowing the length of the transmission line, and measuringthe time for a step or impulse response to return, the dielectricconstant can be calculated. The imaginary part of the dielectricconstant is also found by looking at the loss of the wave, and the finaland initial voltages. Liquid emulators may be ideal for TDR probecalibration. The TDR probes could also be permanently mounted in acylinder of an artificial dielectric mixed with epoxy. Here the TDR rodswould be in contact with the epoxy mix and calibration of the TDR headelectronics and cabling could be achieved.

Calibration Confirmation and Recalibration

As described above, because of variations in manufacturing tolerances,sensing probes, such as electromagnetic devices, of the same design willnot necessarily sense the same reading or same effective dielectricconstant. Consequently, each sensing probe must be individuallycalibrated at the manufacturing factory. Since the response ofelectromagnetic gauges is related to electrical properties of thematerial being tested, it is known that electromagnetic devices mustalso be referenced (calibration confirmed) in the field preferably dailyto account for any daily variances encountered. Furthermore, calibrationof the devices must typically be performed in the field at regularperiodic intervals for determining the absolute density and moisturecontent of materials. It is envisioned that the composite referenceemulators of the present subject matter can be used for gaugecalibration verification and calibration at the operators end (e.g., inthe field).

A single emulator apparatus of the present subject matter (such as thatdescribed above with reference to FIG. 8) can be used to performcalibration confirmation. For example, if an operator measures thereference emulator standard just after calibration of the gauge in thefactory and the standard reading is 150 lbs/ft³, this value becomes thebaseline for all future calibration confirmation readings. If at a latertime, for example several weeks later, the operator again checks thereference emulator standard and the reading is 150.3 lbs/ft³, theoperator knows that the readings must be corrected in order to gatherthe correct density of the material being tested. Based on thesemeasurements, any future readings R by the gauge on the test materialmust be corrected to R−(150.3−150.0) lbs/ft³.

With reference to FIGS. 11A-11C, 12, and 13, a plurality of referenceemulators can be used as a system for field calibration (orrecalibration) of a gauge should a calibration confirmation as describedabove determine that calibration is needed. This recalibration may bedeemed necessary, for example, if a calibration confirmation reading of152.4 lbs/ft³ is obtained, which would indicate that the gauge is “off”by over 2 lbs/ft³ in relation to the 150 lbs/ft³ original baselinestandard. It is understood that any standard criteria, such as 1 lb/ft³,2 lbs/ft³, etc. from a corresponding initial standard baseline reading(e.g., 150 lbs/ft³) may be established for determining whenrecalibration is necessary.

With reference to FIGS. 11A-11C, one embodiment of a calibration systemis shown. Using this system, when a gauge is received from themanufacturer (i.e., after factory calibration), the operator can takemeasurements on an emulator calibrator 200 that consists of, forexample, a set of three reference emulators generally shown as firstemulator 210A, second emulator 210B, and third emulator 210C. Emulators210A, 2106, 210C can be separate or integrated together in one unit.Similar to the apparatus described above with reference to FIG. 8,emulators 210A, 210B, 210C can each comprise an electricallynon-conductive layer (layers 212A, 212B shown in FIGS. 11B and 11C) andan electrically conductive layer (layers 214A, 214B shown in FIGS. 11Band 11C) adjacent the non-conductive layer. As shown in FIG. 11A-11C,emulators 210A, 210B, 210C of emulator calibrator 200 can be of the samethickness but varying in materials of different dielectric constants(thus varying the density values). Alternatively, and as shown in FIG.12, emulators 210A, 2106, 210C of emulator calibrator 200 can be of thesame material (similar dielectric constant) but varying in thickness(thus varying the density values).

Referring back to FIGS. 11A-11C, once measurements are taken onemulators 210A, 210B, 210C, density values D1, D2, D3, respectively, areassigned. Periodically, for example on a daily or weekly basis, theoperator can measure the density values of one or more of emulators210A, 210B, 210C and compare these measured values with the initiallyassigned density values D1, D2, D3. Based on a standard criteria, forexample when the current measurements show a deviation of more than 1lbs/ft³ from the corresponding initial values D1, D2, D3, the operatorcan perform a field calibration using calibrator 200. While calibrationusing a “three block system” is known in the art and described above,the field calibration using calibrator 200 discussed herein involvesplacing the gauge device D on each of emulators 210A, 2106, 210C toobtain new reference measurement readings (FIG. 11B illustrates device Dtaking a reading on first emulator 210A and FIG. 11C illustrates deviceD taking a reading on second emulator 210B). These new readings are thenused in a least squares fit analysis to arrive at new calibrationcoefficients for the gauge. A calibrator system utilizing emulators ofthe present subject matter thereby gives the operator the ability torecalibrate the gauge efficiently in the field without the need to shipthe gauge back to the factory for calibration.

With reference to FIG. 13, a further embodiment of a reference emulatorcalibrator in accordance with the present subject matter is illustratedgenerally as 240. In this embodiment, emulator calibrator 240 compriseselectrically non-conductive layers 242A, 242B, 242C (of the same orvarying thicknesses and of any non-conductive material as discussedabove) joined by a hinged section H. The first non-conductive layer 242Acan have an electrically conductive layer 244 (of any conductivematerial as discussed above) adjacent to it for the emulation of a firstdensity D1. Second non-conductive layer 242B can be placed on firstnon-conductive layer 242A in order to emulate a second density D2 (byincreasing the thickness). Furthermore, third non-conductive layer 242Ccan be placed on second non-conductive layer 242B and firstnon-conductive layer 242A in order to emulate a third density D3 (byincreasing the thickness). In this arrangement, any number of densitiescan be emulated with the use of one conductive layer 244 and a pluralityof non-conductive layers 242A, 242B, 242C. It is understood that whileFIG. 13 illustrates the use of three non-conductive layers 242A, 242B,242C, for the emulation of three different densities D1, D2, D3, anynumber of non-conductive layers could be arranged in a similar manner toemulate varying densities (i.e., two non-conductive layers to emulatetwo densities, four non-conductive layers to emulate four densities,etc.).

It is also understood that the emulator of the present subject mattercan comprise a layered material of alternating non-conductive dielectriclayers and lossy or conductive layers. Alternating layers of dielectricmaterials will show the Maxwell Wagner effect which is a frequencydependent response. This is similar to the Maxwell Wagner effectsexperienced with moist aggregates. It is further envisioned that thenon-conductive dielectric layer in an emulator of the present subjectmatter can comprise holes in order to let gases and/or conductingliquids circulate in order to change the dielectric constants of theemulator. It is further envisioned that the non-conductive dielectriclayer in an emulator of the present subject matter can comprise holes inorder to let gases and/or conducting liquids circulate in order tochange the dielectric constants of the emulator.

Additionally, and with reference to FIG. 14, one embodiment of theemulator of the present subject matter can comprise mechanically movingor mechanically adjustable non-conductive or conductive materials inorder to mimic various dielectric constants. For example, as shown inFIG. 14, a mechanical emulator 310 can comprise an adjustable conductingplate 312 on a moveable piston 314. In this embodiment, anelectromagnetic gauge device D with a sensor 324 sits on one or moresupport columns 322. An air gap AG between sensor 324 and conductingplate 312 acts as the dielectric of the system and as a hand crank ormotor is turned and piston 314 moves upwardly, conducting plate 312 getscloser to the sensor 324 of device D. As such, the energy stored in thedielectric is changed and the effective dielectric constant of thesystem is changed. Conducting plate 312 can be brought toward and awayfrom sensor 324 to simulate various dielectric constants forcalibration. Instead of an air gap, it is envisioned that, as describedabove, the dielectric can be any other suitable non-conductive material(such as plastic) and the mechanical system can involve the moving of aconductive plate towards and away from the dielectric to producedifferent effective dielectric constants.

Artificial Dielectric Cores

An asphalt plant periodically tests the produced asphalt material toverify that the product meets engineering specifications. Often,electromagnetic gauges are used to test asphalt in the field (e.g.,after being laid) to obtain this confirmation. These gauges usually mustbe field off-set from original factory calibration in order to accountfor varying field conditions. Since electromagnetic gauges readdielectric constants and map (relate) this to density, there are twotypical methods used to convert gauge readings to true density values.These methods assume that the gauge reading (R) and the true reading (T)have a linear relationship given by T=m*R+b where m and b are the slopeand the intercept.

In the first method, field data is used to determine a constant toadjust the intercept b. Gauge readings are taken on one or more(preferably three) locations in the middle of an asphalt lane. Cores arethen extracted from these locations and the true density values aredetermined. The gauge and core density readings for the preferable threelocations are classified as (G1, C1), (G2, C2), and (G3, C3). Thedensity difference for the locations are D1, D2, and D3 calculated byD1=G1−C1, D2=G2−C2, and D3=G3−C3. The average density difference is DAcalculated by DA=(D1+D2+D3)/3. The value of DA can then be entered intothe gauge and thereafter the gauge adds the value DA for all readingsgiven by T=R+b+DA.

In the second method, field data is used to determine a project mixspecific slope (m′) and intercept (b′). Gauge readings are taken on twoor more spots in the middle of an asphalt lane as well as close to theedge of the lane. The method further requires extraction anddetermination of actual density of cores from the gauge readinglocations for the off-set calculation.

Both of these methods require the extraction and determination of actualdensity of core samples from the asphalt lane, which is both labor andtime intensive. As such, many asphalt plants produce cylindrical testspecimens using gyratory compactors (known as “pills” or “pucks”). Thesespecimens can be made to have different compaction levels and can beused to determine the mix specific calibration, thereby eliminating theneed for core extraction from the pavement and time delays for obtainingtrue density values. For example, consider that three cylindricalspecimens are made by a gyratory compactor having three density values.If gauge readings are taken on the specimens as G1, G2, and G3 and truedensity values on the specimens are determined to be C1, C2, and C3,then the adjustment to b or a new set of m and b values with a finiteelement correction can be calculated using the calculations of the firstor second method discussed above (without the need for destructiveasphalt cores). Alternatively, a second instrument could be used toobtain the dielectric constant of the cores vs. density, and this can bemapped to the field instrument. The second instrument can be a broadbandcell that measures the bulk electrical properties of the core(throughout the volume of material). The density can also be obtainedusing a dry method such as laser scanning or nuclear analysis such asthe TROXLER COREREADER™.

A gyratory compactor can be used to make laboratory test specimens fromthe field mix materials, such as asphalt and soil with differentmoisture contents. Using the gyro, the method of calibration would be tomake a set of specimens that have a low, medium and high density as afunction of moisture. The dielectric response of these samples couldthen be measured as a function of density, based on moisture over a widefrequency band. This data could be mapped to field instruments for fieldportable sensors, thereby reducing further field analysis. This methodcould aid in correction for specific job site variables such as thebinder type, mineralogy of the mix, aggregate texture, orientation, andsize. Another method of calibration would be to measure the specimenpucks directly with the field instrument in the lab. For example, thefield instrument could be positioned directly on the specimen and ameasurement obtained as a function of density. The field instrumentcould use its own computational efforts to obtain the calibration curvespecific to that material.

In light of the above, there is a long-felt need for the ability toproduce test specimen pucks so that destructive core sampling is notrequired. It is also desired that these test specimens be able to beproduced with known dielectric constants that would emulate dielectricconstants of a known material, such as field mix (asphalt material).

As discussed above, artificial dielectrics are basically large-scalemodels of a dipolar molecule, constructed by arranging conductors in a3-D pattern. A lightweight binder or filler material such as polystyrenesupports the conductors. The result is a manmade material that simulatesan ordinary dielectric material with a dipole moment. The combinedeffect of all the individual conductors of the lattice is to produce anet dipole polarization P per unit volume.

The present subject matter contemplates an artificial dielectric foremulating the dielectric constant of a material, such as for theproduction of a test specimen puck. The artificial dielectric typicallycomprises a substrate matrix having a dielectric constant less than thematerial dielectric constant and an additive combined with thesubstrate, the additive having a dielectric constant higher than thematerial dielectric constant. The substrate can be a material such aspolystyrene or epoxy and can contain voids defining a gas such as air.The additive can consist of conductive metal particles such as metalstrips, disks, needles, spheres, ellipsoids, and cylinders, or a highdielectric powder such as barium titanate, titanium dioxide, and boronnitride.

Referring to FIG. 15, it is envisioned that a plurality of artificialdielectric specimens (three shown generally as AD1, AD2, AD3 in FIG. 15)could be produced wherein dielectric AD1 has a density D1, dielectricAD2 has a different density D2, and dielectric AD3 has a differentdensity D3. These specimens of varying densities could be used for gaugecalibration as described hereinabove. While the test specimen artificialdielectric is preferably in a cylindrical “puck” shape (see FIG. 15), itis understood that the specimen can be a rectangular slab, circular,triangular, or other suitable shape.

REFERENCES

The references listed below are incorporated herein by reference to theextent that they supplement, explain, provide a background for or teachmethodology, techniques and/or processes employed herein. All citedpatent documents and publications referred to in this application areherein expressly incorporated by reference.

W. E. Kock, “Metallic Delay Lines,” Bell System Technical Journal, vol.27, pp. 58-82 (1948);

G. S. Smith and W. R. Scott, Jr., “Antennas and Propagation SocietyInternational Symposium, 1988,” AP-S Digest, pp. 594 and 596 (Jun. 6-10,1988);

G. S. Smith and W. R. Scott, Jr., “The Use of Emulsions to RepresentDielectric Materials in Electromagnetic Scale Models,” IEEE Transactionson Antennas and Propagation, vol. 38, no. 3 (March 1990);

Robert E. Collin, “Field Theory of Guided Waves,” Second Edition, IEEEPress (1991);

ASTM D 7113-05, “Standard Test Method for Density of Bituminous PavingMixtures in Place by the Electromagnetic Surface Contact Methods,” ASTMInternational (2005);

U.S. Pat. No. 5,801,537 for METHOD AND APPARATUS FOR MEASURING IN-PLACESOIL DENSITY AND MOISTURE CONTENT to Siddiqui et al.;

U.S. Pat. No. 5,900,736 for PAVING MATERIAL DENSITY INDICATOR AND METHODUSING CAPACITANCE to Sovik et al.;

U.S. Pat. No. 5,933,015 for METHOD AND APPARATUS FOR MEASURING IN-PLACESOIL DENSITY AND MOISTURE CONTENT to Siddiqui et al.;

U.S. Pat. No. 6,215,317 for METHOD AND APPARATUS FOR MEASURING IN-PLACEDENSITY AND MOISTURE CONTENT to Siddiqui et al.;

U.S. Pat. No. 6,369,381 for APPARATUS AND METHOD FOR CALIBRATION OFNUCLEAR GAUGES to Troxler et al.;

U.S. Pat. No. 6,388,453 for SWEPT-FREQUENCY DIELECTRIC MOISTURE ANDDENSITY SENSOR to Greer;

U.S. Pat. No. 6,400,161 for MATERIAL SEGREGATION AND DENSITY ANALYZINGAPPARATUS AND METHOD to Geisel;

U.S. Pat. No. 6,414,497 for PAVING MATERIAL ANALYZER SYSTEM AND METHODto Sovik et al.;

U.S. Pat. No. 6,677,763 for MATERIAL SEGREGATION, DENSITY, AND MOISTUREANALYZING APPARATUS AND METHOD to Geisel;

U.S. Pat. No. 6,803,771 for PAVING MATERIAL ANALYZER SYSTEM AND METHODto Sovik et al.;

U.S. Patent Application Publication No. 2004/0095154 for ELECTRICALLYMEASURING SOIL DENSITY AND SOIL MOISTURE CONTENT to Lundstrom et al.;and

U.S. Patent Application Publication No. 2005/0150278 for PAVEMENTMATERIAL MICROWAVE DENSITY MEASUREMENT METHODS AND APPARATUSES toTroxier et al.

It will be understood that various details of the presently disclosedsubject matter may be changed without departing from the scope of thepresently disclosed subject matter. Furthermore, the foregoingdescription is for the purpose of illustration only, and not for thepurpose of limitation.

1. A system for calibration of a dielectric sensitive probe to accountfor changes in gauge geometry and other factors affecting gaugecalibration accuracy, the system comprising: (a) a plurality of emulatorapparatuses for emulating electrical characteristics of a plurality ofmaterials having different known dielectric constants, wherein eachemulator apparatus is associated with one of the plurality of materialsand further wherein each emulator apparatus comprises an electricallysimulated layer having a dielectric properties representing theassociated one material dielectric constant; wherein the dielectricsensitive probe is used for the measurement of material selected fromthe group consisting of soil, sand, aggregate, asphalt, cement, andcomposites thereof.
 2. The system for calibration of a dielectricsensitive probe according to claim 1 wherein the electrically simulatedlayer of each emulator apparatus is a plate constructed of materialselected from the group consisting of fiberglass, plastics, ceramics,polymers, glass, and composites thereof.
 3. The system for calibrationof a dielectric sensitive probe according to claim 1 wherein theelectrically simulated layer of each emulator apparatus is a laminateconstructed with a thickness in the range of about 0.375 to 6.000inches.
 4. The system for calibration of a dielectric sensitive probeaccording to claim 1 wherein each emulator apparatus further comprisesan absorbent lossy layer positioned below the electrically simulatedlayer.
 5. The system for calibration of a dielectric sensitive probeaccording to claim 1 wherein the system is used with a dielectricsensitive probe having electrodes mounted for sensing a dielectricconstant adjacent to the probe.
 6. The system for calibration of adielectric sensitive probe according to claim 5 wherein the dielectricsensitive probe is used for the measurement of material selected fromthe group consisting of soil, sand, aggregate, asphalt, cement, andcomposites thereof.
 7. A system for calibration of a dielectricsensitive probe to account for changes in gauge geometry and otherfactors affecting gauge calibration accuracy, the system comprising: (a)a first emulator apparatus for emulating electrical characteristics of afirst material having a known dielectric constant, the first emulatorapparatus comprising: an electrically simulated layer having adielectric constant approximate the first material dielectric constant;and (b) a second emulator apparatus for emulating electricalcharacteristics of a second material having a known dielectric constantdifferent from the dielectric constant of the first material, the secondemulator apparatus comprising: (i) an electrically simulated layerhaving a dielectric constant of about the second material dielectricconstant; and (c) a third emulator apparatus for emulating electricalcharacteristics of a third material having a known dielectric constantdifferent from the dielectric constants of the first and secondmaterials, the third emulator apparatus comprising: (i) an electricallysimulated layer having a dielectric constant of about the third materialdielectric constant; and wherein the electrically simulated layerrepresents pavement materials of one of the groups of soil, sand,aggregate, asphalt, cement, and composites thereof.
 8. The system forcalibration of a dielectric sensitive probe according to claim 7 whereinthe electrically simulated layer of each of the first, second, and thirdemulator apparatuses is a surface constructed of material selected fromthe group consisting of fiberglass, plastics, ceramics, polymers, glass,and composites thereof.
 9. The system for calibration of a dielectricsensitive probe according to claim 7 wherein the electrically simulatedlayer of each of the first, second, and third emulator apparatuses is asurface constructed of an electrically simulated layer with a thicknessin the range of about 0.375 to 6.000 inches.
 10. The system forcalibration of a dielectric sensitive probe according to claim 7 whereineach of the first, second, and third emulator apparatuses furthercomprises an absorbent lossy layer positioned below the electricallysimulated layer.
 11. The system for calibration of a dielectricsensitive probe according to claim 7 wherein the system is used with adielectric sensitive probe having electrodes mounted for sensing adielectric constant adjacent to the probe.
 12. The system forcalibration of a dielectric sensitive probe according to claim 11wherein the dielectric sensitive probe is used for the measurement ofmaterial selected from the group consisting of soil, sand, aggregate,asphalt, cement, and composites thereof.
 13. An emulator apparatus foremulating electrical characteristics of a material having a knowndielectric constant, the emulator apparatus comprising: (a) a firstelectrically non-conductive layer having a dielectric constantapproximately equal to the material dielectric constant; (b) at leastone second electrically non-conductive layer having a dielectricconstant greater than or equal to 1.0, the at least one secondelectrically non-conductive layer adjacent the first non-conductivelayer; and (c) a dielectric sensitive probe used for the measurement ofmaterial selected from the group consisting of soil, sand, aggregate,asphalt, cement, and composites thereof.
 14. A combination carrying caseand emulator apparatus comprising: (a) a housing adapted for containinga dielectric sensitive probe, the housing having a base and a cover; and(b) an emulator apparatus disposed within the housing for emulatingelectrical characteristics of a material having a known dielectricconstant, the emulator apparatus comprising: i. a first electricallynon-conductive layer having a dielectric constant approximately equal tothe material dielectric constant; and ii. at least one secondelectrically non-conductive layer having a dielectric constant greaterthan or equal to 1.0, the at least one second non-conductive layeradjacent the first non-conductive layer; wheras the electricallynon-conductive layers are selected to have properties including thefrequency response of the group consisting of soil, sand, aggregate,asphalt, cement, and composites thereof.